High temperature-resistant coatings have been applied to parts such as automobile engine exhaust headers for years. These coatings are applied to make the parts more attractive and also to help dissipate heat and for corrosion resistance. Corrosion resistance is particularly useful for such applications because metal parts at high temperatures are vulnerable to corrosion, hence the advantage of a coating such as a metallic-ceramic coating. Heretofore, such coatings have needed to be a solid color or other solid appearance because multiple colors or layers could not be accomplished with a single cure.
One problem with applying patterns to a part with ceramic coating relates with the lack of being about to mask areas that have a wet coating. There are also problems associated with a cured coating.
Problems arise when attempting to apply a specific pattern on a wet (uncured) coating. The masking or stenciling materials cannot be used in contact with the uncured, wet ceramic coating surface. The ceramic coatings must be dry enough to apply traditional masking materials, such as tape, without damaging the uncured coating. In addition, the masking material must adhere to part's surface tightly enough to prevent the different coatings to be used in the layers/colors from bleeding together before or during the cure process.
The problem with a cured coating is the inability to coat a second layer over a cured coating and have good adhesion/bonding. Once the ceramic metallic coating has been successfully cured, there are no active bond sites for the next layer of coating to bond to. This condition does not allow for subsequent application of another ceramic coating. If a subsequent application of another ceramic coating is attempted, the result is defects in the coating or coating layers such as blistering, flaking, and peeling of the top coating layer.
Surface preparation on a cured coating layer using a grit blast cabinet can provide rough surface to mechanically bond to by improving the surface area available for the subsequent coating application. This is best accomplished over the entire surface area that was previously coated. However, due to the time involved in the cure process, this method is not favored.
Furthermore, the ability to blend colors & effects with various coatings is not accomplished. The reason this is not accomplished is due to the transition that results from the cured to uncured subsequent interface. This interface will have the defects that applying a coating over a cured ceramic would have. The result would be a coated article that has fissures or crevices between the two coatings.